Just took a look at what Wikipedia has to say about this. You're right, they have a page titled Light Rail, which says it's the same thing as LRT. Their pages for Toronto lines 5 and 6 identify them as light rail.
However, their article on line 3 Scarborough RT identifies it as "light rapid transit" in the infobox, and the phrase links to a page titled Medium-capacity rail system, which "typically resembles a rapid transit system", but doesn't have the word rapid in the label. Hmmm..... Further down the article it does say RT in the name, stands for Rapid Transit.
As for the Ontario line, they call it rapid transit (with 4 citations!) and avoid the LRT abbreviation. The page for Rapid Transit says the term includes MRT mass rapid transit, and RRT rail rapid transit.
Yes, I know Wikipedia is not an authority. But I'm willing to bet their choice of terms has been challenged in the past, and a concensus was reached, undoubtably with input from people on this forum. (But not me!)
But that may not be applicable to the Ontario Line, which could change status when it's actually built.